Reference range of uterine artery Doppler parameters between the 11th and 14th pregnancy weeks in a population sample from Northeast Brazil.

Purpose: To establish reference values for the first trimester uterine artery resistance index (UtA-RI) and pulsatility index (UtA-PI) in healthy singleton pregnant women from Northeast Brazil.

Methods: A prospective observational cohort study including 409 consecutive singleton pregnancies undergoing routine early ultrasound screening at 11 - 14 weeks of gestation was performed. The patients responded to a questionnaire to assess maternal epidemiological characteristics. The left and right UtA-PI and UtA-RI were examined by color and pulsed Doppler by transabdominal technique and the mean UtA-PI, mean UtA-RI and the presence of bilateral protodiastolic notching were recorded. Quartile regression was used to estimate reference values.

Results: The mean ± standard deviation UtA-RI and UtA-PI were 0.7 ± 0.1 and 1.5 ± 0.5, respectively. When segregated for gestation age, mean UtA-PI was 1.6 ± 0.5 at 11 weeks, 1.5 ± 0.6 at 12 weeks, 1.4 ± 0.4 at 13 weeks and 1.3 ± 0.4 at 14 weeks' gestation and mean UtA-RI was 0.7 ± 0.1 at 11 weeks, 0.7 ± 0.1 at 12 weeks, 0.6 ± 0.1 at 13 weeks and 0.6 ± 0.1 at 14 weeks' gestation. Uterine artery bilateral notch was present in 261 (63.8%) patients. We observed that the 5th and 95th percentiles of the UtA-PI and UtA-RI uterine arteries were 0.7 and 2.3 and, 0.5 and 0.8, respectively.

Conclusion: Normal reference range of uterine artery Doppler in healthy singleton pregnancies from Northeast Brazil was established. The 95th percentile of UtA-PI and UtA-RI values may serve as a cut-off for future prediction of pregnancy complications studies (i.e., pre-eclampsia) in Northeast Brazil.